The air-gaps discharge characteristic of UHV AC substation under switching impulse voltage

The minimum air gap distance of UHVAC substation is controlled by the switching pulse voltage. In the past, the minimum air gap distance is decided by the test result under standard switching pulse voltage. The using of long front-time pulse voltage generator can get the air-gaps discharge characteristic, which is more similar in UHVAC system. In this case, the design of UHV substation is not only safe, but also economical. In this paper, the air gap between several typical electrodes and ground in UHVAC substation, including the conductors to ground, the grading ring to ground, is tested under the voltage, whose waveform is standard switching pulse voltage, 1000μs long front-time switching pulse voltage and 2500μs very long front-time switching impulse voltage. The key curve of the air-gaps discharge characteristic is received. The different of discharge voltage under several front-time switching impulse voltages is studied, and the effect of switching pulse voltage's front-time on the discharge voltage of air gap is received. The result shows that the discharge voltage is increasing by the fronttime extending, but growth rate is decreasing by the air gap distance lengthening.